A nonaqueous battery comprises an active material that can easily react with water (e.g., a light metal or its alloy or material capable of intercalating/deintercalating lithium ion) as a negative electrode. Therefore, the nonaqueous battery is arranged such that no water is incorporated in the electrolyte, and the battery container is hermetically sealed to prevent water from entering the battery. The battery container consists of a can or metal member and an insulating sealing material (also referred to as "gasket").
In order to provide perfect sealing, a sealant is provided between the can or metal member and the insulating sealing material. As such sealants, various compounds have been proposed which allegedly can prevent the entry of water and exhibit resistance to an organic solvent contained in the battery as an electricity-generating element. Among these compounds, a pitch (bituminous substance) such as asphalt and coal tar are most widely used. JP-A-56-32671, JP-A-57-194453, JP-A-58-10365, and JP-A-59-859 (The term "JP-A" as used herein means an "unexamined published Japanese patent application") disclose the use of a pitch as the sole sealant. These applications describe that the selection of a sealant having proper physical properties or the coating of such a sealant on the surface of both the metal member and the insulating sealing material renders the battery more resistant to liquid leakage at a temperature as high as 60.degree. C. at a relative humidity of 90%. However, their effects leave much to be desired.
Thus, mixtures of pitch with the following compounds have been proposed. One of these proposals is a mixture of pitch with a mineral oil as disclosed in JP-B-61-36344 (The term "JP-B" as used herein means an "examined Japanese patent publication"). This proposal allegedly provides a further improvement in the resistance of the battery to liquid leakage during storage at a temperature as high as e.g., 60.degree. C. for 100 days or in a 60.degree. C.-minus 10.degree. C. heat cycle. Another proposal is disclosed in JP-A-U-57-194254 (The term "JP-A-U" as used herein means an "unexamined published Japanese utility model application"), JP-A-58-112246, JP-A-59-78443, and JP-A-63-80471 which comprises mixing a pitch with a silicone rubber. This approach allegedly improves the resistance of the battery to liquid leakage during storage at a temperature as high as e.g., 60.degree. C. for 100 days or in a 60.degree. C.-minus 10.degree. C. heat cycle. Further, an approach which comprises mixing a pitch with a thermoplastic or thermosetting resin is proposed in JP-A-59-91660 and JP-A-63-202845. This approach allegedly provides an improvement in the resistance of the battery to liquid leakage during storage at a temperature as high as e.g., 60.degree. C. or 70.degree. C. for 100 days or in a 60.degree. C.-minus 10.degree. C. heat cycle by mixing a pitch with vinyl acetate or atactic polypropylene as a resin. In an approach proposed in JP-B-63-1706, the use of a cationic aqueous dispersion obtained by dispersion-suspending either a pitch (asphalt) or a rubber latex (e.g., styrene-butadiene rubber, butadiene rubber, chloroprene rubber, ethylenepropylene rubber) or a mixture thereof in water with a cationic surface active agent as a sealant allegedly improves in the resistance of the battery to liquid leakage during the storage at a temperature as high as 45.degree. C. at a relative humidity of 90% for 1 to 12 months.
These prior approaches provide an improvement in the resistance of the battery to liquid leakage during the storage at an elevated temperature. However, even these approaches leave much to be desired in the following respects.
The sealing of a nonaqueous battery can be accomplished by pressing a negative electrode can or positive electrode can against an insulating sealing material made of a synthetic resin via a sealant as shown by the reference numerals 12, 13, 14 and 15 in FIG. 2. The strength by which the negative or positive can is pressed against the sealing material is called sealing strength. The sealing strength is affected by the shape of the sealing mold and the molding size of the insulating synthetic resin sealing material or metal member. In particular, the sealing mold is gradually worn away as the sealing process is conducted repeatedly. As a result, the sealing strength is gradually reduced.
On the other hand, a nonaqueous battery is characterized by electricity-generating elements having a high resistance to low temperatures and thus can be used at a temperature as low as -10.degree. C., -30.degree. C., and even -60.degree. C. Once sealing strength is deteriorated, the foregoing nonaqueous batteries have a short resistance to liquid leakage when used at low temperatures.